In the Beginning 49
Ultraviolet (UV) light has shorter wavelengths than visible light.
Though these waves are invisible to the human eye, some insects,
like bumblebees, can see them!
As the wavelengths of light decrease, their energy increases.
Because X-rays have small wavelengths we usually talk about
them in terms of their energy rather than wavelength. Konrad
Rontgen discovered X-rays in 1895 during an experiment with a
ﬂ uorescent plate and a beam of fast electrons in a tube. He dis-
covered that the ﬂ uorescent plate glowed even when it was a long
way from the electron tube and by placing his hand in front of the
ﬂ uorescent plate he created the ﬁ rst X-ray picture. Today, X-rays
are produced in an X-ray tube by ﬁ ring a beam of electrons into a
Tungsten metal target.
Gamma rays have the smallest wavelengths and the most energy
of any other wave in the electromagnetic spectrum. These waves
are generated by radioactive atoms and in nuclear explosions.
Gamma rays can kill living cells and are sometimes used by physi-
cians to kill cancerous cells.
WHAT DOES COLOR HAVE TO DO WITH IT?
Color is a complex phenomenon that has whole books dedicated
to it. The objective here is to gain a very small bit of insight into
what color is and what is involved in portraying color in a video
situation. The signiﬁ cance of color is that the process of transmit-
ting color video involves a great deal of information that will also
50 Digital CCTV
have to be compressed in order to transmit with any useable
speed. In order to transmit color video, the video signal has to
provide extra color information, which consists of a synchroniza-
tion signal, a luminance signal, and a chrominance signal. Mono-
chrome images are concerned only with the ﬁ rst two signals that
provide information about the brightness and coordination of each
line that makes up the frame. These signals are called composite
video because the synchronizing and luminance information are
combined into a lone signal.
The color signal is called a chroma-burst and must be accu-
rately transmitted to the receiving end with no loss of information.
The chrominance portion of the signal tells a video display what
color to reveal. The luminance value adjusts the color to light or
dark, bright or shadowed in order to provide the correct contrast
and color depth. Chrominance is abbreviated with the letter C, and
we already know that luminance is abbreviated with the letter Y.
A chrominance signal requires the transmission of extra data,
which accounts for the larger data ﬁ le related to color.
We have talked about sampling rates and pixels and how
these affect the ﬁ le size, but how is transmission speed affected by
color? Many of the color images we see are not what they seem.
What may appear to be pink, yellow, or black is actually another
optical illusion. Instead of being composed of all the colors that
we perceive, they are made of three primary colors (red, blue, and
green) mixed together. Everything absorbs some of the light that
falls on it, making it appear to be a certain color because it absorbs
all of the light waves except those whose frequency corresponds
to that particular color. Those waves are reﬂ ected back and cause
the eye to see a particular color. The color of an object therefore
depends on the frequency of the electromagnetic wave reﬂ ected.
What we perceive as color is a function of the colors con-
tained in the source of the light that is illuminating what we see
and the colors absorbed and reﬂ ected by the objects upon which
the light falls. Light is focused on a sensitive part within our eyes
containing two kinds of receptors: rods and cones. There are about
100 million rods and about seven million cones. Rods are sensitive
to luminance or black-and-white information. Cones are sensitive
to both luminance and to red, green, or blue color information.